1. Technical Field
The invention relates to vent systems for axles. More particularly, the invention relates to a vent system for axles of heavy-duty vehicles such as trucks and tractor-trailers or semi-trailers. Still more particularly, the invention is directed to an axle vent system that includes a check valve that is mounted on an axle and is in fluid communication with the interior of the axle, and an exhaust tube which is fluidly connected to the check valve. The system relieves pressure build-up in the axle and in a wheel end assembly that is mounted on the axle, while protecting the integrity of the check valve and preventing contaminants from entering the axle and wheel end assembly, thereby extending the life of the components of the wheel end assembly.
2. Background Art
It is to be understood that the axle vent system of the present invention may be employed on heavy-duty vehicles that include tire inflation systems, and on heavy-duty vehicles that do not include tire inflation systems, and that reference herein is made to heavy-duty vehicles with tire inflation systems only by way of example. Heavy-duty vehicles typically include trucks and tractor-trailers or semi-trailers. Tractor-trailers and semi-trailers, which shall collectively be referred to as tractor-trailers for the purpose of convenience, include at least one trailer, and sometimes two or three trailers, all of which are pulled by a single tractor. All heavy-duty vehicles that are trucks or tractor-trailers include multiple tires, each of which is inflated with a fluid or gas, such as air, to an optimum or recommended pressure, which is known in the art as the target pressure.
However, it is well known that air may leak from a tire, usually in a gradual manner, but sometimes rapidly if there is a problem with the tire, such as a defect or a puncture caused by a road hazard. As a result, it is necessary to regularly check the air pressure in each tire to ensure that the tires are not significantly below the target pressure and thus under-inflated. Should an air check show that a tire is under-inflated, it is desirable to enable air to flow into the tire to return it to the target pressure. Likewise, it is well known that the air pressure in a tire may increase due to increases in ambient air temperature, so that it is necessary to regularly check the air pressure in each tire to ensure that the tires are not greatly above the target pressure and thus over-inflated. Should an air check show that a tire is over-inflated, it is desirable to enable air to flow out of the tire to return it to the target pressure.
The large number of tires on any given heavy-duty vehicle setup makes it difficult to manually check and maintain the target pressure for each and every tire. This difficulty is compounded by the fact that trailers of tractor-trailers or trucks in a fleet may be located at a site for an extended period of time, during which the tire pressure might not be checked. Any one of these trailers or trucks might be placed into service at a moment's notice, leading to the possibility of operation with under-inflated or over-inflated tires. Such operation may increase the chance of less-than-optimum performance and/or reduced life of a tire in service as compared to operation with tires at the target pressure, or within an optimum range of the target pressure.
Moreover, should a tire encounter a condition as the vehicle travels over-the-road that causes the tire to become under-inflated, such as developing a leak from striking a road hazard, the life and/or performance of the tire may be significantly reduced if the under-inflation continues unabated as the vehicle continues to travel. Likewise, should a tire encounter a condition that causes it to become significantly over-inflated, such as increasing pressure from an increased ambient air temperature, the life and/or performance of the tire may be significantly reduced if the over-inflation continues unabated as the vehicle continues to travel. The potential for significantly reduced tire life typically increases in vehicles such as trucks or tractor-trailers that travel for long distances and/or extended periods of time under such less-than-optimum inflation conditions.
Such a need to maintain the target pressure in each tire, and the inconvenience to the vehicle operator having to manually check and maintain a proper tire pressure that is at or near the target pressure, led to the development of tire inflation systems. In these systems, a target inflation pressure is selected for the vehicle tires. The system then monitors the pressure in each tire and attempts to maintain the air pressure in each tire at or near the target pressure by inflating the tire when the monitored pressure drops below the target pressure. These prior art tire inflation systems inflate the tires by providing air from the air supply of the vehicle to the tires by using a variety of different components, arrangements, and/or methods. Certain prior art systems are also capable of deflation, and these systems deflate the tires when the monitored pressure rises above the target pressure by venting air from the tires to atmosphere.
One type of arrangement for tire inflation systems involves running a pneumatic supply conduit or line through the axle, which is hollow, to a rotary union that is mounted in the end of the axle spindle or on a hubcap of the wheel end assembly. The rotary union is an airtight rotating seal that enables fluid communication between the non-rotating axle and the rotating tire. Should the supply line experience a leak or rupture, or should the rotary union experience a leak, air pressure may build up in the hollow axle and the wheel end assembly. If the pressure build-up remains unrelieved, components of the wheel end assembly may be damaged.
More particularly, the wheel end assembly typically includes a wheel hub that is rotatably mounted on a bearing assembly, which in turn is immovably mounted on the outboard end of the axle, commonly known as an axle spindle. The bearing assembly includes an inboard bearing and an outboard bearing, which may be separated by a bearing spacer. An axle spindle nut assembly secures the bearing assembly on the axle spindle by threadably engaging threads that are cut into the outer diameter of the outboard end of the axle spindle.
As is well known to those skilled in the art, for normal operation of the wheel end assembly to occur, the bearing assembly and surrounding components must be lubricated with grease or oil. Therefore, the wheel end assembly also must be sealed to prevent leakage of the lubricant, and also to prevent contaminants from entering the assembly, both of which could be detrimental to its performance. More specifically, a hubcap is mounted on an outboard end of the hub adjacent to and outboard from the axle spindle nut assembly, and a main seal is rotatably mounted on an inboard end of the hub in abutment with the axle spindle, resulting in a closed or sealed wheel end assembly.
In the event of a tire inflation system supply line or rotary union leak, there may be a relatively high build-up in air pressure inside the axle and/or wheel end assembly. Such an air pressure build-up may damage the wheel end assembly main seal. If the main seal becomes damaged, it may allow loss of the bearing lubricant, which in turn may undesirably reduce the life of the bearings and/or other components of the wheel end assembly.
In addition, relatively low air pressure build-ups may occur inside an axle and/or wheel end assembly of a heavy-duty vehicle that includes a tire inflation system, and of a heavy-duty vehicle that does not include a tire inflation system. Such low build-ups in air pressure may occur due to any one of multiple causes, such as an increase in ambient temperature, dynamic heating of the components of the wheel end assembly as the vehicle travels, changes in atmospheric pressure when the vehicle travels over roads with significant altitude changes, or a small leak in a supply line if a tire inflation system is employed. Even such a relatively low build-up in air pressure inside the axle and/or wheel end assembly may undesirably reduce the integrity and/or the life of the main seal, which in turn may undesirably reduce the life of the bearings and/or other components of the wheel end assembly.
As a result, it is often desirable to provide an axle and/or wheel end assembly with means for relieving such build-ups of air pressure by venting or exhausting air to atmosphere. Ideally, in order to prevent damage to the wheel end assembly main seal, such means would be capable of exhausting air at a low pressure, so low build-ups in air pressure in the axle and/or wheel end assembly that are due to increases in ambient temperature, dynamic heating of the wheel end assembly, and/or changes in atmospheric pressure remain less than one (1) pound per square inch (psi). In addition, to enable relief of high pressure build-ups to adequately vent the axle and/or wheel end assembly in the event of a tire inflation system supply line or rotary union leak and thus prevent damage to the wheel end assembly main seal, such means would also ideally be capable of high flow of at least about five (5) to ten (10) standard cubic feet per minute (scfm) at a pressure differential of about three (3) psi.
Moreover, when venting or exhausting an air pressure build-up to atmosphere from an axle and/or wheel end assembly, contaminants may be introduced into the wheel end assembly, which may undesirably reduce the life of the bearings and/or other components of the assembly. Therefore, it is also desirable to reduce or minimize the ability of contaminants to enter the wheel end assembly through any vent or exhaust.
In the prior art, certain tire inflation systems have incorporated venting devices in the hubcap to relieve excessive air pressure build-up. However, many of these hubcap venting devices lack the robustness to adequately prevent contaminants from entering the wheel end assembly, which may undesirably reduce the life of the bearings and/or other components of the assembly. More particularly, because these venting devices are incorporated into the hubcap, which is often in an exposed outboard location on the wheel end assembly, the venting devices also are in an exposed location. Such a location enables contaminants, such as water from a high-pressure truck wash, to breach such venting devices and enter the wheel end assembly, thereby reducing the life of the bearings and/or other components of the assembly. In addition, many of these prior art hubcap venting devices lack adequate flow to enable relief of high pressure build-ups in the axle and/or wheel end assembly in the event of a tire inflation system supply line or rotary union leak, thereby allowing the integrity of the wheel end assembly main seal to potentially be compromised.
Other known prior art axle vent devices include vent tubes for drive axles. Vent tubes are often utilized on drive axles because the gears inside the axle generate heat during operation, thus causing the air inside the axle to expand, creating a need to relieve excessive air pressure. Such vent tubes are installed on a drive axle by threading one end of a tube or hose into a corresponding opening formed in the axle. The tube hangs vertically from the axle, with the opposite end of the tube being open to atmosphere. Because the tube is open to atmosphere, such vent tubes typically are not effective in preventing contaminants, such as water, from entering the axle. For example, if a heavy-duty vehicle having such an axle vent tube is backed into a loading dock that is partially submerged in water, the tube may become submerged, which undesirably enables water to enter the axle.
Another known prior art axle vent device involves attaching one end of a rubber hose or tube to a top central portion of an axle, and fastening the hose to the vehicle frame in a manner that allows the hose to extend vertically upwardly from the axle, bend at its highest point, and then wrap back upon itself vertically downwardly. Alternatively, some types of these vent devices are free-standing, rather than being fastened to the vehicle frame, and the downwardly-extending portion of the hose is secured to the upwardly-extending portion by means such as a common tie wrap. However, the end of the hose which is opposite from the end that is attached to the axle is open, and therefore is not effective in preventing contaminants, such as water, from entering the axle. Such axle vent devices enable water to enter the axle if the hose becomes submerged when a heavy-duty vehicle backs into a partially-submerged loading dock.
Still another known prior art axle vent device, which is shown and described in U.S. Pat. No. 6,725,743, and which is owned by the same Assignee as the present invention, Hendrickson USA, L.L.C., involves a tube that is preformed into at least a single loop and is capable of substantially surrounding the axle. One end of the tube is connected to an opening formed in the axle, and the opposite end of the tube includes a check valve to prevent contaminants from entering the axle and wheel end assembly through the vent tube. However, the placement of the check valve on the end of the tube opposite the end that connects to the axle potentially exposes the check valve to undesirable damage from road debris, thereby possibly compromising the integrity of the check valve. If the integrity of the check valve is compromised, contaminants such as moisture may be able to enter the tube and thus impede or obstruct the vent path, particularly if the moisture freezes inside the tube. Also, if the integrity of the check valve is compromised, contaminants may be able to pass through the tube and enter the axle and/or wheel end assembly. Moreover, the preformed-loop tube may be difficult to install and/or adjust, as tightening or rotation of the fitting that provides the connection of the tube to the axle may impeded once the tube surrounds the axle.
Prior art means for relieving the build-up of air pressure in an axle and/or wheel end assembly also often lack the ability to equalize the pressure inside the axle to prevent a vacuum condition from forming inside of the axle and/or wheel end assembly. More particularly, if the means for relieving the build-up of air pressure is unable to allow air to flow from atmosphere into the axle, fluctuations in ambient temperature may create a vacuum condition inside the axle. Such a vacuum condition may undesirably shift the wheel end main seal from its overall position between the axle spindle and the wheel hub, and/or may shift the relative position of the components of the main seal, either of which may compromise the integrity of the main seal and/or reduce its life. It is also desirable to avoid creating a vacuum condition inside the axle and/or the wheel end assembly in order to reduce the possibility that contaminants may be drawn into the axle and/or wheel end assembly by the vacuum. Therefore, it is desirable that the means for relieving the build-up of air pressure also optionally enables the equalization of pressure inside the axle, thereby reducing or minimizing the creation of a vacuum condition inside the axle.
As a result, there is a need in the art for a vehicle axle vent system that relieves pressure build-up in the axle and/or the wheel end assembly and optionally enables the equalization of pressure inside the axle, while protecting the integrity of the check valve, reducing the ability of ice to obstruct the vent path, and preventing contaminants from entering the axle and wheel end assembly, thereby extending the life of the components of the wheel end assembly, and which is easy to install. The vehicle axle vent system of the present invention satisfies these needs, as will be described in detail below.